Method for transmitting and receiving uplink signal in wireless communication system supporting unlicensed band, and apparatus supporting same

ABSTRACT

A method of a user equipment (UE) in a wireless communication system supporting an unlicensed band, includes performing a channel access procedure (CAP) based on a first channel access priority class parameter; receiving, from a base station (BS) a signal including a second channel access priority class parameter and scheduling information for uplink transmission in a specific time resource; performing the CAP based on the first channel access priority class parameter continuously based on that the first channel access priority class parameter is equal to or greater than the second channel access priority class parameter indicated in the signal; performing the CAP based on the second channel access priority class parameter indicated in the signal based on that the first channel access priority class parameter is less than the second channel access priority class parameter; and performing uplink transmission based on a result of the performed CAP.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of co-pending U.S. patent applicationSer. No. 16/071,219 filed on Jul. 19, 2018, which is the National Phaseof PCT International Application No. PCT/KR2017/002517, filed on Mar. 8,2017, which claims priority under 35 U.S.C. 119(e) to U.S. ProvisionalApplication Nos. 62/305,496, filed on Mar. 8, 2016 and 62/315,100, filedon Mar. 30, 2016, all of these applications are hereby expresslyincorporated by reference into the present application.

BACKGROUND OF THE INVENTION Field of the Invention

Following description relates to a wireless communication systemsupporting an unlicensed band, and more particularly, to a method oftransmitting and receiving an uplink signal between a user equipment anda base station in a wireless communication system supporting anunlicensed band and apparatuses supporting the method.

Discussion of the Related Art

Wireless access systems have been widely deployed to provide varioustypes of communication services such as voice or data. In general, awireless access system is a multiple access system that supportscommunication of multiple users by sharing available system resources (abandwidth, transmission power, etc.) among them. For example, multipleaccess systems include a Code Division Multiple Access (CDMA) system, aFrequency Division Multiple Access (FDMA) system, a Time DivisionMultiple Access (TDMA) system, an Orthogonal Frequency Division MultipleAccess (OFDMA) system, and a Single Carrier Frequency Division MultipleAccess (SC-FDMA) system.

When a UE performs LBT (listen-before-talk)-based uplink signaltransmission, an object of the present invention is to provide a methodfor the UE to transmit an uplink signal by efficiently performing anuplink LBT operation.

It will be appreciated by persons skilled in the art that the objectsthat could be achieved with the present disclosure are not limited towhat has been particularly described hereinabove and the above and otherobjects that the present disclosure could achieve will be more clearlyunderstood from the following detailed description.

SUMMARY OF THE INVENTION

The present invention proposes a method of transmitting and receiving anuplink signal between a user equipment and a base station in a wirelesscommunication system supporting an unlicensed band and apparatusessupporting the method.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, accordingto one embodiment, a method of transmitting an uplink signal, which istransmitted by a user equipment (UE) to a base station in a wirelesscommunication system supporting an unlicensed band includes receiving asignal for scheduling uplink transmission in an Nth (N is a naturalnumber) subframe from the base station, if there is a currentlyperformed first LBT (listen-before-talk) prior to the Nth subframe and achannel access priority class of a first LBT parameter for the first LBTis equal to or greater than a channel access priority class of a secondLBT parameter for a second LBT indicated for the Nth subframe,continuously performing the currently performed first LBT, if there isthe currently performed first LBT prior to the Nth subframe and thechannel access priority class of the first LBT parameter for the firstLBT is less than the channel access priority class of the second LBTparameter for the second LBT, performing the second LBT, and performinguplink transmission based on a result of the LBT performed by the UE.

To further achieve these and other advantages and in accordance with thepurpose of the present invention, according to a different embodiment, auser equipment transmitting an uplink signal to a base station in awireless communication system supporting an unlicensed band includes areceiver, a transmitter, and a processor configured to operate in amanner of being connected with the receiver and the transmitter, theprocessor configured to receive a signal for scheduling uplinktransmission in an Nth (N is a natural number) subframe from the basestation, the processor, if there is a currently performed first LBT(listen-before-talk) prior to the Nth subframe and a channel accesspriority class of a first LBT parameter for the first LBT is equal to orgreater than a channel access priority class of a second LBT parameterfor a second LBT indicated for the Nth subframe, configured tocontinuously perform the currently performed first LBT, the processor,if there is the currently performed first LBT prior to the Nth subframeand the channel access priority class of the first LBT parameter for thefirst LBT is less than the channel access priority class of the secondLBT parameter for the second LBT, configured to perform the second LBT,the processor configured to perform uplink transmission based on aresult of the LBT performed by the UE.

In this case, if there is the currently performed first LBT prior to theNth subframe and the channel access priority class of the first LBTparameter for the first LBT is less than the channel access priorityclass of the second LBT parameter for the second LBT, the UE mayterminate the first LBT.

And, when the UE performs the second LBT, it may include initializingoperation of the first LBT performed by the UE and performing the secondLBT.

And, if there is uplink transmission in a subframe before the Nthsubframe, the UE can further perform uplink transmission in the Nthsubframe without an LBT operation.

Technical solutions obtainable from the present invention arenon-limited the above-mentioned technical solutions. And, otherunmentioned technical solutions can be clearly understood from thefollowing description by those having ordinary skill in the technicalfield to which the present invention pertains.

As is apparent from the above description, the embodiments of thepresent disclosure have the following effects.

According to the present invention, a UE receives LBT parameterinformation to transmit an uplink signal to a base station and canperform UL LBT based on the LBT parameter information in a wirelessaccess system supporting an unlicensed band.

In particular, according to the present invention, a UE can perform moreflexible LBT based on LBT parameter information indicated by a basestation and can more efficiently perform uplink transmission based onthe LBT parameter information.

Effects obtainable from the present invention are non-limited by theabove mentioned effect. And, other unmentioned effects can be clearlyunderstood from the following description by those having ordinary skillin the technical field to which the present invention pertains. That is,effects which are not intended by the present invention may be derivedby those skilled in the art from the embodiments of the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, provide embodiments of the presentinvention together with detail explanation. Yet, a technicalcharacteristic of the present invention is not limited to a specificdrawing. Characteristics disclosed in each of the drawings are combinedwith each other to configure a new embodiment. Reference numerals ineach drawing correspond to structural elements.

FIG. 1 is a diagram illustrating physical channels and a signaltransmission method using the physical channels;

FIG. 2 is a diagram illustrating exemplary radio frame structures;

FIG. 3 is a diagram illustrating an exemplary resource grid for theduration of a downlink slot;

FIG. 4 is a diagram illustrating an exemplary structure of an uplinksubframe;

FIG. 5 is a diagram illustrating an exemplary structure of a downlinksubframe;

FIG. 6 is a diagram illustrating an exemplary CA environment supportedin an LTE-Unlicensed (LTE-U) system;

FIG. 7 is a diagram illustrating an exemplary Frame Based Equipment(FBE) operation as one of Listen-Before-Talk (LBT) operations;

FIG. 8 is a block diagram illustrating the FBE operation;

FIG. 9 is a diagram illustrating an exemplary Load Based Equipment (LBE)operation as one of the LBT operations;

FIG. 10 is a diagram for explaining methods of transmitting a DRSsupported in an LAA system;

FIG. 11 is a flowchart for explaining CAP and CWA;

FIG. 12 is a diagram illustrating a partial TTI or a partial subframeapplicable to the present invention;

FIG. 13 is a diagram illustrating an example of a UL LBT operation of aUE according to a method 2 of the present invention;

FIG. 14 is a diagram illustrating a different example of a UL LBToperation of a UE according to a method 2 of the present invention;

FIG. 15 is a diagram illustrating a further different example of a ULLBT operation of a UE according to a method 2 of the present invention;

FIG. 16 is a diagram illustrating a UL LBT operation of a UE accordingto a method 3 of the present invention;

FIG. 17 is a diagram illustrating a UL LBT operation of a UE accordingto a method 4 of the present invention;

FIG. 18 is a diagram illustrating a UL LBT operation of a UE accordingto a method 5 of the present invention;

FIG. 19 is a diagram illustrating a UL LBT operation of a UE accordingto a method 6 of the present invention;

FIG. 20 is a diagram illustrating a UL LBT operation of a UE accordingto a method 7 of the present invention;

FIG. 21 is a diagram illustrating a UL LBT operation of a UE accordingto a method 8 of the present invention;

FIG. 22 is a diagram illustrating a UL LBT operation of a UE accordingto a method 9 of the present invention;

FIG. 23 is a diagram illustrating a UL LBT operation of a UE accordingto a method 10 of the present invention;

FIG. 24 is a diagram illustrating an example of a UL LBT operation of aUE according to a method 11 of the present invention;

FIG. 25 is a diagram illustrating a different example of a UL LBToperation of a UE according to a method 11 of the present invention;

FIG. 26 is a diagram illustrating configurations of a UE and a basestation in which proposed embodiments are implementable.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The embodiments of the present disclosure described below arecombinations of elements and features of the present disclosure inspecific forms. The elements or features may be considered selectiveunless otherwise mentioned. Each element or feature may be practicedwithout being combined with other elements or features. Further, anembodiment of the present disclosure may be constructed by combiningparts of the elements and/or features. Operation orders described inembodiments of the present disclosure may be rearranged. Someconstructions or elements of any one embodiment may be included inanother embodiment and may be replaced with corresponding constructionsor features of another embodiment.

In the description of the attached drawings, a detailed description ofknown procedures or steps of the present disclosure will be avoided lestit should obscure the subject matter of the present disclosure. Inaddition, procedures or steps that could be understood to those skilledin the art will not be described either.

Throughout the specification, when a certain portion “includes” or“comprises” a certain component, this indicates that other componentsare not excluded and may be further included unless otherwise noted. Theterms “unit”, “-or/er” and “module” described in the specificationindicate a unit for processing at least one function or operation, whichmay be implemented by hardware, software or a combination thereof. Inaddition, the terms “a or an”, “one”, “the” etc. may include a singularrepresentation and a plural representation in the context of the presentdisclosure (more particularly, in the context of the following claims)unless indicated otherwise in the specification or unless contextclearly indicates otherwise.

In the embodiments of the present disclosure, a description is mainlymade of a data transmission and reception relationship between a BaseStation (BS) and a User Equipment (UE). A BS refers to a terminal nodeof a network, which directly communicates with a UE. A specificoperation described as being performed by the BS may be performed by anupper node of the BS.

Namely, it is apparent that, in a network comprised of a plurality ofnetwork nodes including a BS, various operations performed forcommunication with a UE may be performed by the BS, or network nodesother than the BS. The term ‘BS’ may be replaced with a fixed station, aNode B, an evolved Node B (eNode B or eNB), an Advanced Base Station(ABS), an access point, etc.

In the embodiments of the present disclosure, the term terminal may bereplaced with a UE, a Mobile Station (MS), a Subscriber Station (SS), aMobile Subscriber Station (MSS), a mobile terminal, an Advanced MobileStation (AMS), etc.

A transmission end is a fixed and/or mobile node that provides a dataservice or a voice service and a reception end is a fixed and/or mobilenode that receives a data service or a voice service. Therefore, a UEmay serve as a transmission end and a BS may serve as a reception end,on an UpLink (UL). Likewise, the UE may serve as a reception end and theBS may serve as a transmission end, on a DownLink (DL).

The embodiments of the present disclosure may be supported by standardspecifications disclosed for at least one of wireless access systemsincluding an Institute of Electrical and Electronics Engineers (IEEE)802.xx system, a 3rd Generation Partnership Project (3GPP) system, a3GPP Long Term Evolution (LTE) system, and a 3GPP2 system. Inparticular, the embodiments of the present disclosure may be supportedby the standard specifications, 3GPP TS 36.211, 3GPP TS 36.212, 3GPP TS36.213, 3GPP TS 36.321 and 3GPP TS 36.331. That is, the steps or parts,which are not described to clearly reveal the technical idea of thepresent disclosure, in the embodiments of the present disclosure may beexplained by the above standard specifications. All terms used in theembodiments of the present disclosure may be explained by the standardspecifications.

Reference will now be made in detail to the embodiments of the presentdisclosure with reference to the accompanying drawings. The detaileddescription, which will be given below with reference to theaccompanying drawings, is intended to explain exemplary embodiments ofthe present disclosure, rather than to show the only embodiments thatcan be implemented according to the disclosure.

The following detailed description includes specific terms in order toprovide a thorough understanding of the present disclosure. However, itwill be apparent to those skilled in the art that the specific terms maybe replaced with other terms without departing the technical spirit andscope of the present disclosure.

For example, the term, TxOP may be used interchangeably withtransmission period or Reserved Resource Period (RRP) in the same sense.Further, a Listen-Before-Talk (LBT) procedure may be performed for thesame purpose as a carrier sensing procedure for determining whether achannel state is idle or busy, CCA (Clear Channel Assessment), and CAP(Channel Access Procedure).

Hereinafter, 3GPP LTE/LTE-A systems are explained, which are examples ofwireless access systems.

The embodiments of the present disclosure can be applied to variouswireless access systems such as Code Division Multiple Access (CDMA),Frequency Division Multiple Access (FDMA), Time Division Multiple Access(TDMA), Orthogonal Frequency Division Multiple Access (OFDMA), SingleCarrier Frequency Division Multiple Access (SC-FDMA), etc.

CDMA may be implemented as a radio technology such as UniversalTerrestrial Radio Access (UTRA) or CDMA2000. TDMA may be implemented asa radio technology such as Global System for Mobile communications(GSM)/General packet Radio Service (GPRS)/Enhanced Data Rates for GSMEvolution (EDGE). OFDMA may be implemented as a radio technology such asIEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Evolved UTRA(E-UTRA), etc.

UTRA is a part of Universal Mobile Telecommunications System (UMTS).3GPP LTE is a part of Evolved UMTS (E-UMTS) using E-UTRA, adopting OFDMAfor DL and SC-FDMA for UL. LTE-Advanced (LTE-A) is an evolution of 3GPPLTE. While the embodiments of the present disclosure are described inthe context of a 3GPP LTE/LTE-A system in order to clarify the technicalfeatures of the present disclosure, the present disclosure is alsoapplicable to an IEEE 802.16e/m system, etc.

1. 3GPP LTE/LTE-A System

In a wireless access system, a UE receives information from an eNB on aDL and transmits information to the eNB on a UL. The informationtransmitted and received between the UE and the eNB includes generaldata information and various types of control information. There aremany physical channels according to the types/usages of informationtransmitted and received between the eNB and the UE.

FIG. 1 illustrates physical channels and a general signal transmissionmethod using the physical channels, which may be used in embodiments ofthe present disclosure.

When a UE is powered on or enters a new cell, the UE performs initialcell search (S11). The initial cell search involves acquisition ofsynchronization to an eNB. Specifically, the UE synchronizes its timingto the eNB and acquires information such as a cell Identifier (ID) byreceiving a Primary Synchronization Channel (P-SCH) and a SecondarySynchronization Channel (S-SCH) from the eNB.

Then the UE may acquire information broadcast in the cell by receiving aPhysical Broadcast Channel (PBCH) from the eNB.

During the initial cell search, the UE may monitor a DL channel state byreceiving a Downlink Reference Signal (DL RS).

After the initial cell search, the UE may acquire more detailed systeminformation by receiving a Physical Downlink Control Channel (PDCCH) andreceiving a Physical Downlink Shared Channel (PDSCH) based oninformation of the PDCCH (S12).

To complete connection to the eNB, the UE may perform a random accessprocedure with the eNB (S13 to S16). In the random access procedure, theUE may transmit a preamble on a Physical Random Access Channel (PRACH)(S13) and may receive a PDCCH and a PDSCH associated with the PDCCH(S14). In the case of contention-based random access, the UE mayadditionally perform a contention resolution procedure includingtransmission of an additional PRACH (S15) and reception of a PDCCHsignal and a PDSCH signal corresponding to the PDCCH signal (S16).

After the above procedure, the UE may receive a PDCCH and/or a PDSCHfrom the eNB (S17) and transmit a Physical Uplink Shared Channel (PUSCH)and/or a Physical Uplink Control Channel (PUCCH) to the eNB (S18), in ageneral UL/DL signal transmission procedure.

Control information that the UE transmits to the eNB is genericallycalled Uplink Control Information (UCI). The UCI includes a HybridAutomatic Repeat and reQuest Acknowledgement/Negative Acknowledgement(HARQ-ACK/NACK), a Scheduling Request (SR), a Channel Quality Indicator(CQI), a Precoding Matrix Index (PMI), a Rank Indicator (RI), etc.

In the LTE system, UCI is generally transmitted on a PUCCH periodically.However, if control information and traffic data should be transmittedsimultaneously, the control information and traffic data may betransmitted on a PUSCH. In addition, the UCI may be transmittedaperiodically on the PUSCH, upon receipt of a request/command from anetwork.

FIG. 2 illustrates exemplary radio frame structures used in embodimentsof the present disclosure.

FIG. 2(a) illustrates frame structure type 1. Frame structure type 1 isapplicable to both a full Frequency Division Duplex (FDD) system and ahalf FDD system.

One radio frame is 10 ms (Tf=307200·Ts) long, including equal-sized 20slots indexed from 0 to 19. Each slot is 0.5 ms (Tslot=15360·Ts) long.One subframe includes two successive slots. An ith subframe includes2ith and (2i+1)th slots. That is, a radio frame includes 10 subframes. Atime required for transmitting one subframe is defined as a TransmissionTime Interval (TTI). Ts is a sampling time given as Ts=1/(15kHz×2048)=3.2552×10−8 (about 33 ns). One slot includes a plurality ofOrthogonal Frequency Division Multiplexing (OFDM) symbols or SC-FDMAsymbols in the time domain by a plurality of Resource Blocks (RBs) inthe frequency domain.

A slot includes a plurality of OFDM symbols in the time domain. SinceOFDMA is adopted for DL in the 3GPP LTE system, one OFDM symbolrepresents one symbol period. An OFDM symbol may be called an SC-FDMAsymbol or symbol period. An RB is a resource allocation unit including aplurality of contiguous subcarriers in one slot.

In a full FDD system, each of 10 subframes may be used simultaneouslyfor DL transmission and UL transmission during a 10-ms duration. The DLtransmission and the UL transmission are distinguished by frequency. Onthe other hand, a UE cannot perform transmission and receptionsimultaneously in a half FDD system.

The above radio frame structure is purely exemplary. Thus, the number ofsubframes in a radio frame, the number of slots in a subframe, and thenumber of OFDM symbols in a slot may be changed.

FIG. 2(b) illustrates frame structure type 2. Frame structure type 2 isapplied to a Time Division Duplex (TDD) system. One radio frame is 10 ms(Tf=307200·Ts) long, including two half-frames each having a length of 5ms (=153600·Ts) long. Each half-frame includes five subframes each being1 ms (=30720·Ts) long. An ith subframe includes 2ith and (2i+1)th slotseach having a length of 0.5 ms (Tslot=15360·Ts). Ts is a sampling timegiven as Ts=1/(15 kHz×2048)=3.2552×10−8 (about 33 ns).

A type-2 frame includes a special subframe having three fields, DownlinkPilot Time Slot (DwPTS), Guard Period (GP), and Uplink Pilot Time Slot(UpPTS). The DwPTS is used for initial cell search, synchronization, orchannel estimation at a UE, and the UpPTS is used for channel estimationand UL transmission synchronization with a UE at an eNB. The GP is usedto cancel UL interference between a UL and a DL, caused by themulti-path delay of a DL signal.

[Table 1] below lists special subframe configurations (DwPTS/GP/UpPTSlengths).

TABLE 1 Normal cyclic prefix in downlink Extended cyclic prefix indownlink UpPTS UpPTS Special Normal Extended Normal Extended subframecyclic prefix cyclic prefix cyclic prefix cyclic prefix configurationDwPTS in uplink in uplink DwPTS in uplink in uplink 0  6592 · T_(s) 2192· T_(s) 2560 · T_(s)  7680 · T_(s) 2192 · T_(s) 2560 · T_(s) 1 19760 ·T_(s) 20480 · T_(s) 2 21952 · T_(s) 23040 · T_(s) 3 24144 · T_(s) 25600· T_(s) 4 26336 · T_(s)  7680 · T_(s) 5  6592 · T_(s) 4384 · T_(s) 5120· T_(s) 20480 · T_(s) 4384 · T_(s) 5120 · T_(s) 6 19760 · T_(s) 23040 ·T_(s) 7 21952 · T_(s) 12800 · T_(s) 8 24144 · T_(s) — — — 9 13168 ·T_(s) — — —

FIG. 3 illustrates an exemplary structure of a DL resource grid for theduration of one DL slot, which may be used in embodiments of the presentdisclosure.

Referring to FIG. 3, a DL slot includes a plurality of OFDM symbols inthe time domain. One DL slot includes 7 OFDM symbols in the time domainand an RB includes 12 subcarriers in the frequency domain, to which thepresent disclosure is not limited.

Each element of the resource grid is referred to as a Resource Element(RE). An RB includes 12×7 REs. The number of RBs in a DL slot, NDLdepends on a DL transmission bandwidth. A structure of an uplink slotmay be identical to a structure of a downlink slot.

FIG. 4 illustrates a structure of a UL subframe which may be used inembodiments of the present disclosure.

Referring to FIG. 4, a UL subframe may be divided into a control regionand a data region in the frequency domain. A PUCCH carrying UCI isallocated to the control region and a PUSCH carrying user data isallocated to the data region. To maintain a single carrier property, aUE does not transmit a PUCCH and a PUSCH simultaneously. A pair of RBsin a subframe is allocated to a PUCCH for a UE. The RBs of the RB pairoccupy different subcarriers in two slots. Thus it is said that the RBpair frequency-hops over a slot boundary.

FIG. 5 illustrates a structure of a DL subframe that may be used inembodiments of the present disclosure.

Referring to FIG. 5, up to three OFDM symbols of a DL subframe, startingfrom OFDM symbol 0 are used as a control region to which controlchannels are allocated and the other OFDM symbols of the DL subframe areused as a data region to which a PDSCH is allocated. DL control channelsdefined for the 3GPP LTE system include a Physical Control FormatIndicator Channel (PCFICH), a PDCCH, and a Physical Hybrid ARQ IndicatorChannel (PHICH).

The PCFICH is transmitted in the first OFDM symbol of a subframe,carrying information about the number of OFDM symbols used fortransmission of control channels (i.e. the size of the control region)in the subframe. The PHICH is a response channel to a UL transmission,delivering an HARQ ACK/NACK signal. Control information carried on thePDCCH is called Downlink Control Information (DCI). The DCI transportsUL resource assignment information, DL resource assignment information,or UL Transmission (Tx) power control commands for a UE group.

2. LTE-U System

2.1 LTE-U System Configuration

Hereinafter, methods for transmitting and receiving data in a CAenvironment of an LTE-A band corresponding to a licensed band and anunlicensed band will be described. In the embodiments of the presentdisclosure, an LTE-U system means an LTE system that supports such a CAstatus of a licensed band and an unlicensed band. A WiFi band orBluetooth (BT) band may be used as the unlicensed band. LTE-A systemoperating on an unlicensed band is referred to as LAA (Licensed AssistedAccess) and the LAA may correspond to a scheme of performing datatransmission/reception in an unlicensed band using a combination with alicensed band.

FIG. 6 illustrates an example of a CA environment supported in an LTE-Usystem.

Hereinafter, for convenience of description, it is assumed that a UE isconfigured to perform wireless communication in each of a licensed bandand an unlicensed band by using two CCs. The methods which will bedescribed hereinafter may be applied to even a case where three or moreCCs are configured for a UE.

In the embodiments of the present disclosure, it is assumed that acarrier of the licensed band may be a primary CC (PCC or PCell), and acarrier of the unlicensed band may be a secondary CC (SCC or SCell).However, the embodiments of the present disclosure may be applied toeven a case where a plurality of licensed bands and a plurality ofunlicensed bands are used in a carrier aggregation method. Also, themethods suggested in the present disclosure may be applied to even a3GPP LTE system and another system.

In FIG. 6, one eNB supports both a licensed band and an unlicensed band.That is, the UE may transmit and receive control information and datathrough the PCC which is a licensed band, and may also transmit andreceive control information and data through the SCC which is anunlicensed band. However, the status shown in FIG. 6 is only example,and the embodiments of the present disclosure may be applied to even aCA environment that one UE accesses a plurality of eNBs.

For example, the UE may configure a macro eNB (M-eNB) and a PCell, andmay configure a small eNB (S-eNB) and an SCell. At this time, the macroeNB and the small eNB may be connected with each other through abackhaul network.

In the embodiments of the present disclosure, the unlicensed band may beoperated in a contention-based random access method. At this time, theeNB that supports the unlicensed band may perform a Carrier Sensing (CS)procedure prior to data transmission and reception. The CS proceduredetermines whether a corresponding band is reserved by another entity.

For example, the eNB of the SCell checks whether a current channel isbusy or idle. If it is determined that the corresponding band is idlestate, the eNB may transmit a scheduling grant to the UE to allocate aresource through (E)PDCCH of the PCell in case of a cross carrierscheduling mode and through PDCCH of the SCell in case of aself-scheduling mode, and may try data transmission and reception.

At this time, the eNB may configure a TxOP including N consecutivesubframes. In this case, a value of N and a use of the N subframes maypreviously be notified from the eNB to the UE through higher layersignaling through the PCell or through a physical control channel orphysical data channel.

2.2 Carrier Sensing (CS) Procedure

In embodiments of the present disclosure, a CS procedure may be called aClear Channel Assessment (CCA) procedure. In the CCA procedure, it maybe determined whether a channel is busy or idle based on a predeterminedCCA threshold or a CCA threshold configured by higher-layer signaling.For example, if energy higher than the CCA threshold is detected in anunlicensed band, SCell, it may be determined that the channel is busy oridle. If the channel is determined to be idle, an eNB may start signaltransmission in the SCell. This procedure may be referred to as LBT.

FIG. 7 is a view illustrating an exemplary Frame Based Equipment (FBE)operation as one of LBT operations.

The European Telecommunication Standards Institute (ETSI) regulation (EN301 893 V1.7.1) defines two LBT operations, Frame Based Equipment (FBE)and Load Based Equipment (LBE). In FBE, one fixed frame is comprised ofa channel occupancy time (e.g., 1 to 10ms) being a time period duringwhich a communication node succeeding in channel access may continuetransmission, and an idle period being at least 5% of the channeloccupancy time, and CCA is defined as an operation for monitoring achannel during a CCA slot (at least 20 μs) at the end of the idleperiod.

A communication node periodically performs CCA on a per-fixed framebasis. If the channel is unoccupied, the communication node transmitsdata during the channel occupancy time. On the contrary, if the channelis occupied, the communication node defers the transmission and waitsuntil the CCA slot of the next period.

FIG. 8 is a block diagram illustrating the FBE operation.

Referring to FIG. 8, a communication node (i.e., eNB) managing an SCellperforms CCA during a CCA slot. If the channel is idle, thecommunication node performs data transmission (Tx). If the channel isbusy, the communication node waits for a time period calculated bysubtracting the CCA slot from a fixed frame period, and then resumesCCA.

The communication node transmits data during the channel occupancy time.Upon completion of the data transmission, the communication node waitsfor a time period calculated by subtracting the CCA slot from the idleperiod, and then resumes CCA. If the channel is idle but thecommunication node has no transmission data, the communication nodewaits for the time period calculated by subtracting the CCA slot fromthe fixed frame period, and then resumes CCA.

FIG. 9 is a view illustrating an exemplary LBE operation as one of theLBT operations.

Referring to FIG. 9(a), in LBE, the communication node first sets q (q ∈{4, 5, . . . , 32}) and then performs CCA during one CCA slot.

FIG. 9(b) is a block diagram illustrating the LBE operation. The LBEoperation will be described with reference to FIG. 9(b).

The communication node may perform CCA during a CCA slot. If the channelis unoccupied in a first CCA slot, the communication node may transmitdata by securing a time period of up to (13/32)q ms.

On the contrary, if the channel is occupied in the first CCA slot, thecommunication node selects N (N ∈ {1, 2, . . . , q}) arbitrarily (i.e.,randomly) and stores the selected N value as an initial count. Then, thecommunication node senses a channel state on a CCA slot basis. Each timethe channel is unoccupied in one specific CCA slot, the communicationnode decrements the count by 1. If the count is 0, the communicationnode may transmit data by securing a time period of up to (13/32)q ms.

2.3 Discontinuous Transmission in DL

When discontinuous transmission is performed on an unlicensed carrierhaving a limited maximum transmission period, the discontinuoustransmission may influence on several functions necessary for performingan operation of LTE system. The several functions can be supported byone or more signals transmitted at a starting part of discontinuous LAADL transmission. The functions supported by the signals include such afunction as AGC configuration, channel reservation, and the like.

When a signal is transmitted by an LAA node, channel reservation has ameaning of transmitting signals via channels, which are occupied totransmit a signal to other nodes, after channel access is performed viaa successful LBT operation.

The functions, which are supported by one or more signals necessary forperforming an LAA operation including discontinuous DL transmission,include a function for detecting LAA DL transmission transmitted by a UEand a function for synchronizing frequency and time. In this case, therequirement of the functions does not mean that other availablefunctions are excluded. The functions can be supported by other methods.

2.3.1 Time and Frequency Synchronization

A design target recommended by LAA system is to support a UE to make theUE obtain time and frequency synchronization via a discovery signal formeasuring RRM (radio resource management) and each of reference signalsincluded in DL transmission bursts, or a combination thereof. Thediscovery signal for measuring RRM transmitted from a serving cell canbe used for obtaining coarse time or frequency synchronization.

2.3.2 DL Transmission Timing

When a DL LAA is designed, it may follow a CA timing relation betweenserving cells combined by CA, which is defined in LTE-A system (Rel-12or earlier), for subframe boundary adjustment. Yet, it does not meanthat a base station starts DL transmission only at a subframe boundary.Although all OFDM symbols are unavailable in a subframe, LAA system cansupport PDSCH transmission according to a result of an LBT operation. Inthis case, it is required to support transmission of control informationnecessary for performing the PDSCH transmission.

2.4 Measuring and Reporting RRM

LTE-A system can transmit a discovery signal at a start point forsupporting RRM functions including a function for detecting a cell. Inthis case, the discovery signal can be referred to as a discoveryreference signal (DRS). In order to support the RRM functions for LAA,the discovery signal of the LTE-A system and transmission/receptionfunctions of the discovery signal can be applied in a manner of beingchanged.

2.4.1 Discovery Reference Signal (DRS)

A DRS of LTE-A system is designed to support on/off operations of asmall cell. In this case, off small cells correspond to a state thatmost of functions are turned off except a periodic transmission of aDRS. DRSs are transmitted at a DRS transmission occasion with a periodof 40, 80, or 160 ms. A DMTC (discovery measurement timingconfiguration) corresponds to a time period capable of anticipating aDRS received by a UE. The DRS transmission occasion may occur at anypoint in the DMTC. A UE can anticipate that a DRS is continuouslytransmitted from a cell allocated to the UE with a correspondinginterval.

If a DRS of LTE-A system is used in LAA system, it may bring newconstraints. For example, although transmission of a DRS such as a veryshort control transmission without LBT can be permitted in severalregions, a short control transmission without LBT is not permitted inother several regions. Hence, a DRS transmission in the LAA system maybecome a target of LBT.

When a DRS is transmitted, if LBT is applied to the DRS, similar to aDRS transmitted in LTE-A system, the DRS may not be transmitted by aperiodic scheme. In particular, it may consider two schemes described inthe following to transmit a DRS in the LAA system.

As a first scheme, a DRS is transmitted at a fixed position only in aDMTC configured on the basis of a condition of LBT.

As a second scheme, a DRS transmission is permitted at one or moredifferent time positions in a DMTC configured on the basis of acondition of LBT.

As a different aspect of the second scheme, the number of time positionscan be restricted to one time position in a subframe. If it is moreprofitable, DRS transmission can be permitted at the outside of aconfigured DMTC as well as DRS transmission performed in the DMTC.

FIG. 10 is a diagram for explaining DRS transmission methods supportedby LAA system.

Referring to FIG. 10, the upper part of FIG. 10 shows the aforementionedfirst scheme for transmitting a DRS and the bottom part of FIG. 10 showsthe aforementioned second scheme for transmitting a DRS. In particular,in case of the first scheme, a UE can receive a DRS at a positiondetermined in a DMTC period only. On the contrary, in case of the secondscheme, a UE can receive a DRS at a random position in a DMTC period.

In LTE-A system, when a UE performs RRM measurement based on DRStransmission, the UE can perform single RRM measurement based on aplurality of DRS occasions. In case of using a DRS in LAA system, due tothe constraint of LBT, it is difficult to guarantee that the DRS istransmitted at a specific position. Even though a DRS is not actuallytransmitted from a base station, if a UE assumes that the DRS exists,quality of an RRM measurement result reported by the UE can bedeteriorated. Hence, when LAA DRS is designed, it is necessary to permitthe existence of a DRS to be detected in a single DRS occasion. By doingso, it may be able to make the UE combine the existence of the DRS withRRM measurement, which is performed on successfully detected DRSoccasions only.

Signals including a DRS do not guarantee DRS transmissions adjacent intime. In particular, if there is no data transmission in subframesaccompanied with a DRS, there may exist OFDM symbols in which a physicalsignal is not transmitted. While operating in an unlicensed band, othernodes may sense that a corresponding channel is in an idle state duringa silence period between DRS transmissions. In order to avoid theabovementioned problem, it is preferable that transmission burstsincluding a DRS signal are configured by adjacent OFDM symbols in whichseveral signals are transmitted.

2.5 Channel Access Procedure and Contention Window Adjustment Procedure

In the following, the aforementioned channel access procedure and thecontention window adjustment procedure are explained in the aspect of atransmission node.

FIG. 11 is a flowchart for explaining CAP and CWA.

In order for an LTE transmission node (e.g., a base station) to operatein LAA Scell(s) corresponding to an unlicensed band cell for DLtransmission, it may initiate a channel access procedure (CAP) [S1110].

The base station can randomly select a back-off counter N from acontention window (CW). In this case, the N is configured by an initialvalue Ninit [S1120]. The Ninit is randomly selected from among valuesranging from 0 to CWp.

Subsequently, if the back-off counter value (N) corresponds to 0[S1122], the base station terminates the CAP and performs Tx bursttransmission including PSCH [S1124]. On the contrary, if the back-offvalue is not 0, the base station reduces the back-off counter value by 1[S1130].

The base station checks whether or not a channel of the LAA Scell(s) isin an idle state [S1140]. If the channel is in the idle state, the basestation checks whether or not the back-off value corresponds to 0[S1150]. The base station repeatedly checks whether or not the channelis in the idle state until the back-off value becomes 0 while reducingthe back-off counter value by 1.

In the step S1140, if the channel is not in the idle state i.e., if thechannel is in a busy state, the base station checks whether or not thechannel is in the idle state during a defer duration (more than 15 usec)longer than a slot duration (e.g., 9 usec) [S1142]. If the channel is inthe idle state during the defer duration, the base station can resumethe CAP [S1144]. For example, when the back-off counter value Ninitcorresponds to 10, if the channel state is determined as busy after theback-off counter value is reduced to 5, the base station senses thechannel during the defer duration and determines whether or not thechannel is in the idle state. In this case, if the channel is in theidle state during the defer duration, the base station performs the CAPagain from the back-off counter value 5 (or, from the back-off countervalue 4 by reducing the value by 1) rather than configures the back-offcounter value Ninit. On the contrary, if the channel is in the busystate during the defer duration, the base station performs the stepS1142 again to check whether or not the channel is in the idle stateduring a new defer duration.

Referring back to FIG. 11, the base station checks whether or not theback-off counter value (N) becomes 0 [S1150]. If the back-off countervalue (N) becomes 0, the base station terminates the CAP and may be ableto transmit a Tx burst including PDSCH.

The base station can receive HARQ-ACK information from a UE in responseto the Tx burst [S1170]. The base station can adjust a CWS (contentionwindow size) based on the HARQ-ACK information received from the UE[S1180].

In the step S1180, as a method of adjusting the CWS, the base stationcan adjust the CWS based on HARQ-ACK information on a first subframe ofa most recently transmitted Tx burst (i.e., a start subframe of the Txburst).

In this case, the base station can set an initial CW to each priorityclass before the CWP is performed. Subsequently, if a probability thatHARQ-ACK values corresponding to PDSCH transmitted in a referencesubframe are determined as NACK is equal to or greater than 80%, thebase station increases CW values set to each priority class to a nexthigher priority.

In the step S1160, PDSCH can be assigned by a self-carrier schedulingscheme or a cross-carrier scheduling scheme. If the PDSCH is assigned bythe self-carrier scheduling scheme, the base station counts DTX,NACK/DTX, or ANY state among the HARQ-ACK information fed back by the UEas NACK. If the PDSCH is assigned by the cross-carrier schedulingscheme, the base station counts the NACK/DTX and the ANY states as NACKand does not count the DTX state as NACK among the HARQ-ACK informationfed back by the UE.

If bundling is performed over M (M>=2) number of subframes and bundledHARQ-ACK information is received, the base station may consider thebundled HARQ-ACK information as M number of HARQ-ACK responses. In thiscase, it is preferable that a reference subframe is included in the Mnumber of bundled subframes.

3. Proposed Embodiment

When a base station or a UE performs LBT (listen-before-talk)-basedsignal transmission in a wireless communication system consisting of thebase station and the UE, the present invention proposes a detaildownlink transmission method.

According to the present invention, a base station or a UE shouldperform LBT to transmit a signal on an unlicensed band. When the basestation or the UE transmits a signal, it is necessary to make signalinterference not to be occurred with different communication nodes suchas Wi-Fi, and the like. For example, according to Wi-Fi standard, a CCAthreshold value is regulated by −62 dBm and −82 dBm for a non-Wi-Fisignal and a Wi-Fi signal, respectively. In particular, if an STA(station) or an AP (access point) senses a signal received with power(or energy) equal to or greater than −62 dBm rather than Wi-Fi, the STAor the AP does not perform signal transmission.

In this case, it may be difficult to always guarantee DL transmission ofan eNB or UL transmission of a UE on an unlicensed. Hence, a UEoperating on the unlicensed band may maintain access with a differentcell operating on a licensed band to stably control mobility, RRM (radioresource management) function, and the like. In the present invention,for clarity, a cell accessed by a UE on the unlicensed band is referredto as a U-S cell (or LAA S cell) and a cell accessed by the UE on thelicensed band is referred to as a Pcell. As mentioned in the foregoingdescription, a scheme of performing data transmission/reception on theunlicensed band using a combination with the licensed band is generallycalled LAA (licensed assisted access).

TABLE 2 Channel Access Priority Class (p) m_(p) CW_(min,p) CW_(max,p)T_(m cot,p) allowed CW_(p) sizes 1 1  3   7 2 ms {3, 7} 2 1  7  15 3 ms{7, 15} 3 3 15  63 8 or 10 {15, 31, 63} ms 4 7 15 1023 8 or 10 {15, 31,63, 127, ms 255, 511, 1023}

As shown in Table 2, in Rel-13 LAA system, 4 channel access priorityclasses are defined in total. And, a length of a defer period, a CWS,MCOT (maximum channel occupancy time), and the like are definedaccording to each of the channel access priority classes. Hence, when aneNB transmits a downlink signal via an unlicensed band, the eNB performsrandom backoff by utilizing LBT parameters determined according to achannel access priority class and may be then able to access a channelduring limited maximum transmission time only after the random backoffis completed.

For example, in case of the channel access priority class 1/2/3/4, themaximum channel occupancy time (MCOT) is determined by 2/3/8/8 ms. Themaximum channel occupancy time (MCOT) is determined by 2/3/10/10 ms inenvironment where other RAT such as Wi-Fi does not exists (e.g., bylevel of regulation).

As shown in Table 2, a set of CWSs capable of being configured accordingto a class is defined. One of points different from Wi-Fi system is inthat a different backoff counter value is not defined according to achannel access priority class and LBT is performed using a singlebackoff counter value (this is referred to as single engine LBT).

For example, when an eNB intends to access a channel via an LBToperation of class 3, since CWmin (=15) is configured as an initial CWS,the eNB performs random backoff by randomly selecting an integer fromamong numbers ranging from 0 to 15. If a backoff counter value becomes0, the eNB starts DL Tx and randomly selects a new backoff counter for anext Tx burst after the DL Tx burst is completed. In this case, if anevent for increasing a CWS is triggered, the eNB increases a size of theCWS to 31 corresponding to a next size, randomly selects an integer fromamong numbers ranging from 0 to 31, and performs random backoff.

In this case, when a CWS of the class 3 is increased, CWSs of allclasses are increased as well. In particular, if the CW of the class 3becomes 31, a CWS of a class 1/2/4 becomes 7/15/31. If an event fordecreasing a CWS is triggered, CWS values of all classes are initializedby CWmin irrespective of a CWS value of the triggering timing.

FIG. 12 is a diagram illustrating a partial TTI or a partial subframeapplicable to the present invention.

In Rel-13 LAA system, MCOT is utilized as much as possible when DL Txburst is transmitted. In order to support consecutive transmission, apartial TTI, which is defined as DwPTS, is introduced. The partial TTI(or partial subframe) corresponds to a section in which a signal istransmitted as much as a length shorter than a legacy TTI (e.g., 1 ms)when PDSCH is transmitted.

In the present invention, for clarity, a starting partial TTI or astarting partial subframe corresponds to a form that a part of symbolspositioned at the fore part of a subframe are emptied out. An endingpartial TTI or an ending partial subframe corresponds to a form that apart of symbols positioned at the rear part of a subframe are emptiedout. (On the contrary, an intact TTI is referred to as a normal TTI or afull TTI.)

FIG. 12 illustrates various types of the aforementioned partial TTI. Thefirst drawing of FIG. 12 illustrates an ending partial TTI (or subframe)and the second drawing illustrates a starting partial TTI (or subframe).The third drawing of FIG. 12 illustrates a partial TTI (or subframe)that a part of symbols positioned at the fore part and the rear part ofa subframe are emptied out. In this case, when signal transmission isexcluded from a normal TTI, a time section during which the signaltransmission is excluded is referred to as a transmission gap (TX gap).

Although the present invention is explained on the basis of a DLoperation in FIG. 12, the present invention can also be identicallyapplied to a UL operation. For example, a partial TTI structure shown inFIG. 12 can be applied to a form of transmitting PUCCH or PUSCH as well.

LTE Rel-14 system supports UL transmission in LAA. To this end, it maybe able to define channel access priority class for the UL transmissionas well. Similar to DL LBT of LTE Rel-13 LAA, if a UE performs a UL LBToperation based on an LBT parameter according to a specific channelaccess priority class X to transmit a UL TX burst, the UE can transmitonly UL traffic corresponding to a channel access priority class Y equalto or higher than the channel access priority class X (i.e., Y≤X) onPUSCH within the UL TX burst. In this case, if there is no UL trafficcorresponding to the channel access priority class Y, the UE maytransmit UL traffic corresponding to a channel access priority class Zhaving a priority lower than the channel access priority X.

The present invention proposes a method for a user equipment toconfigure a UL TX burst using channel access priority class informationconfigured according to a scheduled UL subframe, a method of configuringCOT and MCOT, and a method for the UE to configure a UL TX burst usingan LBT parameter and TX gap information. In the following description,for clarity, a channel access priority class is referred to as an LBTpriority class. In this case, as a value of the LBT priority class isgetting bigger, it may indicate that a priority is getting lower. In thefollowing description, for clarity, although operations of the presentinvention are explained on the basis of LTE system, the operations ofthe present invention can be applied to any wireless communicationsystem performing LBT-based transmission.

3.1 Method of Configuring LBT Priority Class for UL TX Burst

3.1.1 Method 1

A base station can configure an LBT priority class including informationon an LBT parameter (defer time, a CW size, MCOT, etc.) or types (e.g.,best effort, VoIP, etc.) of UL traffic capable of being transmitted in acorresponding UL subframe for all UL subframes scheduled via a UL grant(or common DCI). In this case, if the base station performsmulti-subframe scheduling based on a single UL grant, LBT priority classinformation included in the UL grant can be applied to all of aplurality of scheduled subframes.

In this case, when an LBT priority class is set to a specific ULsubframe, a UE may be able to transmit UL traffic corresponding to anLBT priority class equal to or higher than the LBT priority class set tothe specific UL subframe via PUSCH or may be able to perform PUCCHtransmission. If the UL traffic does not exist, the UE can transmit ULtraffic corresponding to an LBT priority class lower than the LBTpriority class set to the specific UL subframe.

As mentioned in the foregoing description, discussion on an LAA ULoperation is in progress in LTE Rel-14 system. In particular, when abase station transmits a UL grant via a U-Scell (e.g., self-carrierscheduling case), the base station schedules PUSCH transmission for aplurality of UL subframes in a single DL subframe. In particular,discussion on a multi-subframe scheduling method is in progress tomitigate control overhead of the UL grant transmission.

As an example of configuring LBT priority class for a UL TX burst, abase station indicates a UE to transmit a UL TX burst via themulti-subframe scheduling and can indicate a lowest LBT priority classof the UL TX burst. According to the method, since the base stationalways indicates the UL TX burst using the multi-subframe scheduling,single subframe scheduling can be utilized for transmitting a single ULsubframe only. In particular, it may set a limit on a UL schedulingmethod of the base station.

Hence, preferably, if the base station configures an LBT priority classaccording to a UL subframe, the UE can configure a UL TX burst based oninformation on the LBT priority class configured according to the ULsubframe. In this case, the base station can configure an LBT priorityclass according to each UL subframe via a UL grant. If the base stationperforms multi-subframe scheduling via a single UL grant, since themulti-subframe scheduling is performed for the purpose of ULtransmission within the same UL TX burst, single LBT priority classinformation within the UL grant can be commonly applied to themulti-subframes.

Meanwhile, in order to make the base station configure an LBT priorityclass, the UE can ask the base station to transmit information on an LBTpriority class to be scheduled to the UE in advance. If the base stationdoes not configure an LBT priority class, the UE can autonomouslyconfigure an LBT priority class for a UL subframe scheduled by the basestation.

3.1.2 Method 2

If PUSCH (or PUCCH) transmitted by a UE does not exist immediatelybefore the UE transmits PUSCH (or PUCCH) within a specific UL subframe,the UE performs LBT before the UE transmits the PUSCH within the ULsubframe. If the UE succeeds in occupying a channel, the UE starts totransmit a UL signal and configures a (used) UL COT, UL MCOT, and alowest LBT priority class (for a UL TX burst) as follows.

(1) The UE can configure a (used) UL COT as follows.

1) If an LBT operation follows an LBT priority class set to the specificUL subframe, the UE can configure time ranging from a start point of theUL signal to the end of PUSCH transmission within the UL subframe as the(used) UL COT.

2) If an LBT operation is not related to an LBT priority class set tothe specific UL subframe (e.g., fixed LBT or single CCA slot-based LBT),the UE can configure time ranging from a start point of a DL TX burstincluding a UL grant, which has scheduled PUSCH included in the ULsubframe, to the end of PUSCH transmission within the UL subframe as the(used) UL COT. In other word, the UE can configure a time periodincluding DL COT+DTX as the UL COT.

In case of the 2), if a signal is not transmitted during a time periodranging from the start point of the DL TX burst to the start point ofthe UL signal, the time period can be excluded from the UL COT.

Or, in case of the 2), if the DL TX burst includes UL grants only, theUE can configure a time period ranging from the start point of the ULsignal to the end of PUSCH transmission within the UL subframe as the(used) UL COT.

(2) The UE can configure MCOT within an LBT priority class, which is setto a UL subframe in which the PUSCH (or PUCCH) is transmitted, as the ULMCOT.

(3) The UE can configure an LBT priority class set to a UL subframe inwhich the PUSCH (or PUCCH) is transmitted as a lowest LBT priority class(for a UL TX burst).

When the (used) UL MCOT is configured, it may consider a UL signalincluding a reservation signal.

The lowest LBT priority class (for the UL TX burst) may indicate that acorresponding UL subframe is included in the UL TX burst only when anLBT priority class set to a following UL subframe has a priority equalto or higher than the lowest LBT priority class.

When an LBT priority class is configured according to a UL subframescheduled by the base station, the UE performs UL LBT by applying LBTparameters according to an LBT priority class set to a corresponding ULsubframe to transmit a first PUSCH (or PUCCH) within a UL TX burst. Ifthe UE succeeds in transmitting the first PUSCH (or PUCCH), the UE canconsider the LBT priority class as the lowest LBT priority class of theUL TX burst to be continuously transmitted.

FIG. 13 is a diagram illustrating an example of a UL LBT operation of aUE according to a method 2 of the present invention. As shown in FIG.13, if there exists PUSCH to be transmitted in a UL subframe to which anLBT priority class 3 is set, a UE can perform UL LBT by applying LBTparameters according to the LBT priority class 3 prior to the ULsubframe.

As mentioned in the foregoing description, discussion on a method ofutilizing DL MCOT at the time of performing LAA UL transmission is inprogress in LTE Rel-14 system. Specifically, when a base stationtransmits a DL TX burst, if there is a remaining period among a timeperiod corresponding to DL MCOT, a UE may be able to transmit a UL TXburst in the remaining period based on a fixed UL LBT (e.g., single CCAslot-based LBT) operation which is advantageous for accessing a channelcompared to a general UL LBT operation. In this case, the UL TX burstinherits DL MCOT and the base station can set the lowest LBT priorityclass of the DL TX burst to a UL subframe in which the first PUSCH (orPUCCH) is transmitted within the UL TX burst.

In this case, the UE configures the LBT priority class set to thesubframe in which the first PUSCH (or PUCCH) is transmitted within theUL TX burst as the lowest LBT priority class of the UL TX burst. The UEcan perform a fixed UL LBT operation instead of a UL LBT operationcorresponding to the lowest LBT priority class. In this case, in orderto inform the UE of an operation to be performed by the UE among the ULLBT operation according to the lowest LBT priority class and the fixedUL LBT operation, the base station can indicate the operation via a ULgrant or common DCI.

FIG. 14 is a diagram illustrating a different example of a UL LBToperation of a UE according to a method 2 of the present invention. Asshown in FIG. 14, if a UL TX burst borrows DL MCOT, or if the UL TXburst is transmitted within the DL MCOT, a UE performs a fixed LBT(e.g., single CCA slot-based LBT) operation to transmit the UL TX burst.

In this case, if the DL TX burst includes UL grants only, the UE canconfigure a time period ranging from a start point of a DL TX burst tothe end of PUSCH transmission within the UL subframe as UL COT. Or, inorder to exclude transmission delay due to UL timing from UL COT, the UEcan configure the sum of a length of a reservation signal and a PUSCHtransmission length within the UL subframe as the UL COT.

FIG. 15 is a diagram illustrating a further different example of a ULLBT operation of a UE according to a method 2 of the present invention.A difference between the FIG. 14 and FIG. 15 is in that COT used fortransmitting a UL grant and a period during which a signal is nottransmitted until UL signal is transmitted after the UL grant istransmitted are excluded from the UL COT.

In the method 2 proposed in the present invention, if PUSCH (or PUCCH)transmitted by a UE does not exist immediately before PUSCH (or PUCCH)is transmitted in the specific UL subframe, it may indicate that a ULsignal to be transmitted in a UL subframe prior to the specific ULsubframe does not exist. Or, it may indicate an ending partial TTI whilea UL signal to be transmitted in a UL subframe prior to the specific ULsubframe exists. Or, it may indicate that a type of a UL signal to betransmitted in the specific subframe corresponds to a starting partialTTI. If a UE performs UL TX burst transmission in a UL subframe to whicha LBT priority class is not set within DL MCOT of a previous DL TXburst, the UE may assume that the lowest LBT priority class of the UL TXburst is identical to the lowest LBT priority class of the DL TX burst.

3.2 UL TX Burst Configuration Method of (LBT Priority Class-Based) UE

3.2.1 Method 3

If PUSCH (or PUCCH) transmitted by a UE exists immediately before the UEtransmits PUSCH (or PUCCH) within a specific UL subframe, the UE mayoperate as follows according to a relationship between the lowest LBTpriority class (X1) (for a UL TX burst) and an LBT priority class (X2)for the specific UL subframe.

(1) If the LBT priority class set to the UL subframe is equal to orhigher than the lowest LBT priority class (for the UL TX burst) (i.e.,X1≥X2),

(1)-1) If a length of the sum of the (used) UL COT prior to the ULsubframe and a PUSCH (or PUCCH) transmission length within the ULsubframe is equal to or less than UL MCOT, the UE performs the PUSCH (orPUCCH) transmission within the UL subframe without LBT and can updatethe (used) UL COT length with the length of the sum.

(1)-2) If the length of the sum of the (used) UL COT prior to the ULsubframe and the PUSCH (or PUCCH) transmission length within the ULsubframe is greater than UL MCOT, the UE can perform initialization onthe (used) UL COT, the UL MCOT, and the lowest LBT priority class (forthe UL TX burst). If PUSCH transmission is omitted in the UL subframe ora starting partial TTI is supported, the UE can perform the operationmentioned earlier in the method 2.

(2) If the LBT priority class set to the UL subframe is lower than thelowest LBT priority class (for the UL TX burst) (i.e., X1<X2),

(2)-1) The UE can perform the same operation mentioned earlier in the(1)-2).

More specifically, if the UE succeeds in transmitting a first PUSCH (orPUCCH) of a UL TX burst, the UE can configure UL COT, UL MCOT, and thelowest LBT priority class for the UL TX burst according to the operationmentioned earlier in the method 2. In this case, the UE can include(consecutive) UL subframes having an LBT priority class equal to orhigher than the lowest LBT priority class (for the UL TX burst) in theUL TX burst within a range not exceeding the UL MCOT.

For example, when a UE is scheduled to transmit PUSCH (or PUCCH) in annth UL subframe within a UL TX burst and is scheduled to continuouslytransmit the PUSCH (or PUCCH) in an (n+1)th UL subframe, the UE mayconsider two conditions described in the following to determine whetherto include the (n+1)th UL subframe in the UL TX burst.

1> When a length of the PUSCH (or PUCCH or UL signal) to be transmittedwithin the (n+1)th UL subframe is reflected to UL COT, whether or notthe total transmission length exceeds UL MCOT

2> Whether a priority of an LBT priority class set to the (n+1)th ULsubframe is equal to or greater than the lowest LBT priority class forthe UL TX burst

If at least one of the two conditions is not satisfied, the UEdetermines that the UL TX burst is ended. The UE performs initializationon the (used) UL COT for the UL TX burst, UL MCOT, and the lowest LBTpriority class (for the UL TX burst) and may be then able to attempt totransmit a new UL TX burst.

FIG. 16 is a diagram illustrating a UL LBT operation of a UE accordingto a method 3 of the present invention.

As shown in FIG. 16, when UL subframe transmission corresponds to an LBTpriority class of a priority lower than the lowest LBT priority class(for a UL TX burst), a UE does not include the UL subframe transmissionin the UL TX burst (e.g., omit PUSCH transmission). As mentioned earlierin the method 2 of the present invention, it may be able to configure anew UL TX burst.

3.2.2 Method 4

A UE transmits PUSCH (or PUCCH) in a specific UL subframe and may bethen able to perform one of operations described in the following in atime period not including a UL signal to be transmitted by the UE.

(1) The US performs initialization on (used) UL COT, UL MCOT, and lowestLBT priority class (for UL TX burst).

(2) The UE updates (used) UL COT. If the UL COT reaches UL MCOT, the UEperforms initialization.

(2)-1) If (used) UL COT is less than UL MCOT, the UE updates a length ofthe (used) UL COT by adding a time period not including signaltransmission to the (used) UL COT and can maintain the UL MCOT and thelowest LBT priority class (for the UL TX burst).

(2)-2) If (used) UL COT becomes identical to UL MCOT, the UE can performinitialization on the (used) UL COT, the UL MCOT, and the lowest LBTpriority class (for UL TX burst).

(3) The UE maintains (used) UL COT, UL MCOT, and lowest LBT priorityclass (for UL 6 TX burst).

The operation mentioned earlier in the (2) of the method 4 of thepresent invention can be applied to a case that a length of the timeperiod not including signal transmission is equal to or less than aspecific length only.

More specifically, unlike DL transmission, UL transmission depends onscheduling of a base station in LTE system. Hence, it may also consideran operation for terminating UL TX burst of a UE. In particular, if abase station directly indicates a TX gap within a UL subframe, it may beable to terminate a UL TX burst of a UE.

FIG. 17 is a diagram illustrating a UL LBT operation of a UE accordingto a method 4 of the present invention.

As shown in FIG. 17, although a specific UE (e.g., UE1) has UL trafficto transmit, a base station configures a TX gap to perform FDM(frequency division multiplexing) or MU-MIMO (multi-user input multioutput) operation with a different UE (e.g., UE2) in a following ULsubframe. By doing so, the base station can terminate a UL TX burst ofthe specific UE (e.g., UE1) before UL COT reaches UL MCOT.

In this case, when the UE configures the UL TX burst, if the UE iscontacted with a time period where signal transmission does not exist,the UE assumes that the UL TX burst is terminated in the time period andmay be able to initialize (used) UL COT for the UL TX burst, UL MCOT,and the lowest LBT priority class. Then, the UE performs a new UL LBToperation on a UL TX burst to be transmitted after the timing to whichthe TX gap is set by the base station. Or, if a UE utilizes a timeperiod corresponding to previously secured UL MCOT for transmitting anext UL TX burst, the UE may not initialize the (used) UL COT, the ULMCOT, and the lowest LBT priority class. Instead, the time period notincluding signal transmission can be additionally reflected to the(used) UL COT. In particular, although the UE does not perform signaltransmission during prescribed time, the UE can perform UL transmissionin a time period included in the UL COT without a new LBT.

3.2.3 Method 5

If PUSCH (or PUCCH) transmitted by a UE does not exist immediatelybefore the UE transmits PUSCH (or PUCCH) within a specific UL subframeand specific values are maintained without initializing (used) UL COT,UL MCOT, and the lowest LBT priority class (for a UL TX burst), the UEmay operate as follows according to a relationship between the lowestLBT priority class (X1) (for the UL TX burst) and an LBT priority class(X2) for the specific UL subframe. In other word, the method 5 of thepresent invention can be applied to a case that the UE does notinitialize the (used) UL COT, the UL MCOT, and the lowest LBT priorityclass mentioned earlier in the method 4.

(1) If the LBT priority class set to the UL subframe is equal to orhigher than the lowest LBT priority class (for the UL TC burst) (i.e.,X1≥X2)

(1)-1) If a length of the sum of the (used) UL COT prior to the ULsubframe and a PUSCH (or PUCCH) transmission length within the ULsubframe is equal to or less than UL MCOT, the UE attempts to transmitthe PUSCH (or PUCCH) within the UL subframe according to a fixed LBToperation and can update the (used) UL COT length with the length of thesum (if the UE succeeds in transmitting the PUSCH (or PUCCH)).

(1)-2) If the length of the sum of the (used) UL COT prior to the ULsubframe and the PUSCH (or PUCCH) transmission length within the ULsubframe is greater than UL MCOT, the UE can perform initialization onthe (used) UL COT, the UL MCOT, and the lowest LBT priority class (forthe UL TX burst). Or, the UE may perform the operation mentioned earlierin the method 2.

(2) If the LBT priority class set to the UL subframe is lower than thelowest LBT priority class (for the UL TX burst) (i.e., X1<X2),

(2)-1) The UE can perform the same operation mentioned earlier in the(1)-2) of the method 5.

More specifically, as mentioned earlier in the method 4, it may considera method for a UE to utilize a time period corresponding to previouslysecured UL MCOT for transmitting a next UL TX burst. As an example ofthe method, when the UE transmits a new UL TX burst within the remainingUL MCOT period among the time period corresponding to the UL MCOTsecured by the UE, the UE can perform a UL LBT operation of which an LBTparameter is mitigated (or a fixed LBT operation or an LBT operationirrespective of an LBT priority class). In this case, the UE can include(consecutive) UL subframes having an LBT priority class equal to orhigher than the lowest LBT priority class (for the UL TX burst) in theUL TX burst within a range not exceeding the remaining UL MCOT periodfor the new UL TX burst.

FIG. 18 is a diagram illustrating a UL LBT operation of a UE accordingto a method 5 of the present invention.

As shown in FIG. 18, a UE can operate according to the aforementionedmethod 4. In this case, if PUSCH (or PUCCH) transmitted by the UE doesnot exist immediately before PUSCH (or PUCCH) is transmitted in thespecific UL subframe, it may indicate that a UL signal to be transmittedin a UL subframe prior to the specific UL subframe does not exist. Or,it may indicate an ending partial TTI while a UL signal to betransmitted in a UL subframe prior to the specific UL subframe exists.Or, it may indicate that a type of a UL signal to be transmitted in thespecific subframe corresponds to a starting partial TTI.

3.2.4 Method 6

When a base station transmits a UL grant within a time periodcorresponding to DL MCOT of a previously transmitted DL TX burst, if atransmission signal of the base station does not exist before the ULgrant is transmitted, the base station can transmit the UL grantaccording to a fixed LBT operation (or an LBT operation irrespective ofan LBT priority class).

As mentioned in the foregoing description, discussion on a method ofutilizing DL MCOT for performing LAA UL transmission is in progress inLTE-Rel-14 system. In this case, it may consider a method of utilizingDL COT not only for transmitting a UL TX burst but also for transmittinga UL grant. In particular, a base station can transmit a UL grant basedon a fixed DL LBT (e.g., single CCA slot-based LBT) operation which isadvantageous for accessing a channel compared to a general UL LBToperation in the remaining period remained after a DM TX burst istransmitted among a time period corresponding to the DL MCOT.

FIG. 19 is a diagram illustrating a UL LBT operation of a UE accordingto a method 6 of the present invention.

As shown in FIG. 19, a base station performs a fixed LBT to transmit aUL grant within DL MCOT and may be then able to transmit the UL grant.

3.3 UL TX Burst Configuration Method of (LBT Parameter and TX GapInformation-Based) UE

3.3.1 Method 7

If a base station informs a UE of whether to apply an LBT parameter(e.g., CWS, backoff counter, etc.) and a TX gap according to a scheduledUL subframe, the UE can configure a UL TX burst as follows.

(1) If PUSCH (or PUCCH) transmitted by a UE does not exist immediatelybefore the UE transmits PUSCH (or PUCCH) within a specific UL subframe,the UE can perform an LBT parameter-based LBT operation set to the ULsubframe prior to the UL subframe.

(2) If PUSCH (or PUCCH) transmitted by a UE exists immediately beforethe UE transmits PUSCH (or PUCCH) within a specific UL subframe, the UEcan perform PUSCH (or PUCCH) transmission in the specific subframewithout an LBT operation.

(3) If a UE has no UL signal to transmit (e.g., empty SF or TX gap), theUE stops configuring a current UL TX burst and may be able to configurea new UL TX burst. In this case, a TX gap can be applied to timingindicated by a base station only.

In this case, when a UL TX burst is transmitted based on a specific LBTparameter, a base station may set a limit on scheduling in order not topermit a case that a length of the UL TX burst is to be longer than ULMCOT for the specific LBT parameter.

More specifically, when the base station controls the UL MCOT in theaspect of scheduling, if the base station transmits an indication on anLBT parameter according to a UL subframe and indication on a TX gap tothe UE, the UE can configure a UL TX burst via the indicationinformation. In this case, it is not necessary for the UE to consider acase that UL MCOT of the UE exceeds UL MCOT.

FIG. 20 is a diagram illustrating a UL LBT operation of a UE accordingto a method 7 of the present invention.

More specifically, when a base station schedules 4 consecutive ULsubframes and 1 UL subframe including a Tx gap at a fore part appearingimmediately after the 4 consecutive UL subframes in time domain and a UEfails to detect a UL grant for a first UL subframe among the 4consecutive UL subframes, FIG. 21 illustrates an operation of the UE.

As illustrated in FIG. 20, the UE starts to transmit a UL TX burstaccording to the (1) of the method 7 prior to a second UL subframe amongthe 4 consecutive UL subframes and can configure a UL TX burst including3 consecutive UL subframes according to the (2) of the method 7.However, since a TX gap is positioned at the fore part of a 5thscheduled UL subframe, the UE stops configuring a previously configuredUL TX burst according to the (3) of the method 7 and may be then able toattempt to transmit a new UL TX burst.

3.3.2 Method 8

If a base station informs a UE of an LBT parameter (e.g., CWS, backoffcounter, etc.) according to a scheduled UL subframe and information onwhether to perform a new LBT, the UE can configure a UL TX burst asfollows.

(1) If PUSCH (or PUCCH) transmitted by a UE does not exist immediatelybefore the UE transmits PUSCH (or PUCCH) within a specific UL subframe,the UE can perform an LBT parameter-based LBT operation set to the ULsubframe prior to the UL subframe. In this case, the UE may assume thata TX gap is applied to the fore part of the UL subframe (or a rear partof a UL subframe immediately before the UL subframe).

(2) If PUSCH (or PUCCH) transmitted by a UE exists immediately beforethe UE transmits PUSCH (or PUCCH) within a specific UL subframe, the UEcan transmit PUSCH (or PUCCH) in the specific subframe without an LBToperation.

(3) If a UE has no UL signal to transmit or a new LBT performanceindication indicates that a new UL TX burst starts, the UE stopsconfiguring a current UL TX burst and may be able to configure a new ULTX burst.

In this case, when a base station configures an LBT parameter for aspecific UL subframe, it may be able to set a limit on UL scheduling toprevent a UE from performing UL transmission more than UL MCOTcorresponding to the LBT parameter.

More specifically, similar to the aforementioned method 7, when the basestation controls the UL MCOT in the aspect of scheduling, if the basestation transmits an indication on an LBT parameter according to a ULsubframe and indication on whether to perform a new LBT to the UE, theUE can configure a UL TX burst via the indication information.

In this case, a TX gap can be applied to the timing at which a new LBTis to be performed (e.g., a fore part of time domain of a first ULsubframe within the UL TX burst or a rear part of time domain of a ULsubframe immediately before the first UL subframe). The timing maycorrespond to a position promised between the base station and the UE(e.g., a fore part of time domain of a first UL subframe within the ULTX burst).

Or, a TX gap indication of the base station may indicate the performanceof a new LBT. As an example of indicating whether or not the new LBT isperformed, it may apply a scheme that the base station toggles 1 bitinformation included in a UL grant (or common DCI) at the timing atwhich a new UL TX burst starts. Or, the base station indicates ‘1’ for asubframe in which new LBT is to be performed and indicates ‘0’ for asubframe in which whether to perform LBT is determined by the UE usingthe 1 bit information.

FIG. 21 is a diagram illustrating a UL LBT operation of a UE accordingto a method 8 of the present invention.

More specifically, when a base station schedules 4 consecutive ULsubframes and 1 UL subframe including a TX gap at a fore part appearingimmediately after the 4 consecutive UL subframes in time domain and a UEfails to detect a UL grant for a first UL subframe among the 4consecutive UL subframes, FIG. 21 illustrates an operation of the UE.

As illustrated in FIG. 21, if a UE fails to detect a UL grant for afirst UL subframe among the 4 consecutive UL subframes, the UE may applya TX gap to the fore part of a second UL subframe. Subsequently, the UEtransmits PUSCH in the second subframe to a fourth UL subframe and maybe able to transmit PUSCH by applying a separate TX gap to a fifthsubframe and performing LBT.

3.3.3 Method 9

If a base station informs a UE of an LBT parameter (e.g., CWS, backoffcounter, etc.) according to a scheduled UL subframe, information onwhether or not a TX gap is applied, and information on UL MCOT, the UEcan configure a UL TX burst as follows.

(1) If PUSCH (or PUCCH) transmitted by a UE does not exist immediatelybefore the UE transmits PUSCH (or PUCCH) within a specific UL subframe,the UE can perform an LBT parameter-based LBT operation set to the ULsubframe prior to the UL subframe.

(2) If PUSCH (or PUCCH) transmitted by a UE exists immediately beforethe UE transmits PUSCH (or PUCCH) within a specific UL subframe, the UEcan transmit PUSCH (or PUCCH) in the specific subframe without an LBToperation under the condition of not exceeding UL MCOT.

(3) If a UE has no UL signal to transmit or UL MCOT is all utilized, theUE stops configuring a current UL TX burst and may be able to configurea new UL TX burst. In this case, the UE can selectively apply a TX gapindicated by a base station. In other word, the UE may not apply the TXgap within the UL MCOT.

In FIGS. 20 and 21, if an LBT parameter corresponding to Set 2 is ableto support UL MCOT 4 ms, a UE may be able to configure a UL TX burst byutilizing the UL MCOT as much as possible.

Or, when a base station indicates a UE to apply a TX gap in a specificUL subframe, if the UE determines that it is not necessary for the UE toapply the TX gap because the UL subframe is fully included in UL MCOT,the UE may not apply the TX gap. In particular, whether to apply the TXgap can be determined by the UE.

FIG. 22 is a diagram illustrating a UL LBT operation of a UE accordingto a method 9 of the present invention.

FIG. 22 illustrates an example of a method 9. When a base stationschedules 4 consecutive UL subframes and 1 UL subframe including a TXgap at a fore part appearing immediately after the 4 consecutive ULsubframes in time domain and a UE fails to detect a UL grant for a firstUL subframe among the 4 consecutive UL subframes, FIG. 22 illustrates anoperation of the UE.

As shown in FIG. 22, if a UE fails to detect a UL grant for a first ULsubframe, the UE can continuously transmit PUSCH in a second to fifth ULsubframes without applying any separate TX gap.

As a variation of the method 9 of the present invention, when a UEconfigures a UL TX burst based on an LBT parameter (e.g., CWS, backoffcounter, etc.) according to a UL subframe, information on whether or nota TX gap is applied, and information on UL MCOT indicated by a basestation, the UE may always follow an indication of the base station todetermine whether or not a TX gap is applied in a UL subframe whileperforming the operations of (1) and (2) of the method 9. In particular,it may consider a method of combining (1) and (2) of the method 9 with(3) of the method 7.

3.3.4 Method 10

If a base station informs a UE of an LBT parameter (e.g., CWS, backoffcounter, etc.) according to a scheduled UL subframe and information onUL MCOT, the UE can configure a UL TX burst as follows.

(1) If PUSCH (or PUCCH) transmitted by a UE does not exist immediatelybefore the UE transmits PUSCH (or PUCCH) within a specific UL subframe,the UE can perform an LBT operation prior to the UL subframe. In thiscase, the UE may assume that a TX gap is applied to the fore part of theUL subframe (or a rear part of a UL subframe immediately before the ULsubframe)

(2) If PUSCH (or PUCCH) transmitted by a UE exists immediately beforethe UE transmits PUSCH (or PUCCH) within a specific UL subframe, the UEcan transmit PUSCH (or PUCCH) in the specific subframe without an LBToperation under the condition of not exceeding UL MCOT.

More specifically, as a variation according to the combination of themethod 8 and the method 9, it may indicate the LBT parameter accordingto a UL subframe and the UL MCOT information only and it may notindicate information on whether or not a TX gap is applied.

In this case, the UE may assume that a TX gap is applied to the forepart of the UL subframe in which a first PUSCH (or PUCCH) of a UL TXburst is transmitted or a rear part of a UL subframe immediately beforethe UL subframe.

FIG. 23 is a diagram illustrating a UL LBT operation of a UE accordingto a method 10 of the present invention.

More specifically, when a base station schedules 4 consecutive ULsubframes and 1 UL subframe including a TX gap at a fore part appearingimmediately after the 4 consecutive UL subframes in time domain and a UEfails to detect a UL grant for a first UL subframe among the 4consecutive UL subframes, FIG. 23 illustrates an operation of the UE.

As illustrated in FIG. 23, if a UE fails to detect a UL grant for afirst UL subframe among the 4 consecutive UL subframes, the UE may applya TX gap to the fore part of a second UL subframe. Subsequently, the UEmay continuously transmit PUSCH in the second subframe to a fifth ULsubframes.

3.3.5 Method 11

When a base station indicates an LBT parameter set A to a specific ULsubframe, if PUSCH (or PUCCH) transmitted by a UE does not existimmediately before the UE transmits PUSCH (or PUCCH) within the specificUL subframe, the UE can perform UL LBT as follows before the PUSCH(PUCCH) is transmitted within the UL subframe.

(1) If the UE does not perform UL LBT, the UE can perform UL LBT basedon the LBT parameter set A set to the specific UL subframe.

(2) If the UE performs UL LBT based on an LBT parameter set B, it mayselect one from among options described in the following.

(2)-1) The UE can continuously perform the currently operating UL LBToperation.

(2)-2) If the set B is different from the set A, the UE can perform ULLBT based on the set A. Otherwise, the UE can continuously perform thecurrently operating UL LBT operation.

(2)-3) If the set A has longer UL MCOT, a bigger backoff counter (or CCAsection), or a bigger CW size compared to the set B, the UE can performUL LBT based on the set A. Otherwise, the UE can continuously performthe currently operating UL LBT operation.

(2)-4) If the set A has less remaining backoff counters (or CCA section)compared to the set B, the UE can perform UL LBT based on the set A.Otherwise, the UE can continuously perform the currently operating ULLBT operation.

In this case, when the UE intends to perform UL LBT based on an LBTparameter set to a specific UL subframe, the UL LBT can be performedafter previous UL LBT operations are initialized when PUSCH (PUCCH)transmission fails in a previous UL subframe.

FIG. 24 is a diagram illustrating an example of a UL LBT operation of aUE according to a method 11 of the present invention.

In FIG. 24, assume that an LBT parameter set 1 supports 4 ms UL MCOT, anLBT parameter set 2 supports 2 ms UL MCOT, and a CCS section required bythe set 2 is shorter than a CCA section required by the set 1. In thiscase, a base station can sequentially configure set 1/set 1/set 2/set 2according to a UL subframe while scheduling 4 consecutive UL subframes.

As shown in FIG. 24, if a UE fails to detect a UL grant from the first 2UL subframes, the UE can perform UL LBT based on a set 2 LBT parameterset to the third UL subframe according to the (1) of the method 11. Theoperation above is useful in that it is able to use UL LBT requiringless CCA section in accordance with the UL COT 2 ms to be actuallytransmitted by the UE.

FIG. 25 is a diagram illustrating a different example of a UL LBToperation of a UE according to a method 11 of the present invention.

When the UE performs UL LBT according to the set 1 prior to the first ULsubframe, if the UE fails to transmit PUSCH (or PUCCH) in the first ULsubframe and the second UL subframe, as shown in FIG. 25, the UE cantransmit PUSCH (PUCCH) in the third UL subframe using the previouslyperformed set 1-based UL LBT according to the (2)-1) of the method 11without using the set 2 set to the third UL subframe.

3.3.6 Method 12

A base station indicates an LBT parameter set A for a specific ULsubframe and a timing capable of applying the LBT parameter set A forthe specific UL subframe can be configured by a timing appearing beforea start timing (or a start timing of PUSCH transmission within the ULsubframe) of the specific UL subframe as much as TLBT.

In this case, a base station can set the TLBT to a UE using one ofmethods described in the following.

(1) The base station sets a TLTB value to the UE via higher layersignaling.

(2) The base station sets a plurality of TLTB values to the UE viahigher layer signaling, selects a TLTB value from among a plurality ofthe TLTB values via a UL grant (or common DCI), and can indicate theselected TLTB value to the UE.

(3) The base station can indicate a TLTB value via a UL grant (or commonDCI).

(4) A TLTB can be defined by a predetermined value.

Additionally, it may be able to set a limit on the UE to make the UEperform UL LBT for the specific UL subframe within a time period rangingfrom the timing to which the LBT parameter set A is applicable to thestart of a UL signal in the UL subframe only.

In this case, the TLBT can be configured to have a length shorter than alength of a single SF.

For example, the base station can configure the UE to start an UL LBToperation for the specific UL subframe from a timing appearing prior tothe start timing of the specific UL subframe as much as one symbol. Inthis case, the UE can apply an LBT parameter set indicated by the basestation to the specific UL subframe. If the UE fails to transmit PUSCHin the specific UL subframe, the UE can initialize a UL LBT operationfrom the timing at which the PUSCH transmission fails. When an LBTparameter set is indicated to a specific UL subframe, the base stationis able to set a time period capable of performing a UL LBT operationusing the LBT parameter set to the UE. In this case, the LBT parameterset-based UL LBT operation set to the specific UL subframe can beperformed until a UL signal is transmitted in the UL subframe. If aseparate ending timing is not determined, the LBT parameter set-based ULLBT operation can be performed for a UL signal to be transmitted later.

3.3.7 Method 13

When a base station indicates an LBT parameter set A and a timing atwhich the LBT parameter set A is applicable for a specific UL subframe,if there is a separate UL LBT operation performed until the timing atthe timing at which the LBT parameter set A is applicable, a UEsubtracts the number of currently accumulated idle CCA slots and may beable to perform an LBT parameter set A-based UL LBT operation.

For example, when an LBT parameter set A for a specific UL subframe isapplied, assume that there is a UL LBT previously performed until thetiming to which the LBT parameter set A is applied and 10 idle CCA slotsare examined in the previous UL LBT procedure. In this case, if abackoff counter value according to the LBT parameter set A correspondsto 16, a UE can reflect the examined 10 idle CCA slots to the backoffcounter value. In particular, the UE can perform an LBT parameter setA-based UL LBT operation with a backoff counter value of 6 (=16-10).

If the number of idle CCA slots examined in a previous UL LBT procedureis greater than the backoff counter value of the LBT parameter set A,the UE assumes that the backoff counter value corresponds to 0 and maybe able to immediately transmit a reservation signal. Or, the UE canperforms a self-defer operation to maintain the backoff counter value by0 while continuously examining idle CCA slots until the timing at whichPUSCH transmission starts within the specific UL subframe. In this case,if a busy CCA slot is examined in the middle of performing theself-defer operation, the UE may resume the LBT parameter set A-based ULLBT operation.

3.3.8 Method 14

A UE selects an LBT parameter corresponding to a length of a UL TX burst(or an MCOT value including the length of the UL TX burst) to betransmitted by the UE and may be able to perform an UL LBT operation byapplying the selected LBT parameter.

In this case, if a base station indicates an LBT parameter to transmitthe UL TX burst, the UE performs an LBT parameter-based UL LBT accordingto the indication of the base station. If the UE fails to perform ULtransmission, the UE can perform the operation mentioned earlier in themethod 14.

For example, when a base station indicates a UE to transmit a UL TXburst, the base station can inform the UE of an LPT parameter fortransmitting the UL TX burst. In this case, although the UE hasperformed the LBT parameter-based UL LBT indicated by the base station,the UE assumes that the UE has failed to transmit UL subframespositioned at the fore part of the UL TX burst.

In this case, in the aspect of the UE, the LBT parameter indicated bythe base station may correspond to an LBT parameter requiring excessivebackoff operations compared to a length of the remaining UL TX burst.

More specifically, assume that a base station indicates a UE to transmita UL TX burst including 8 UL subframes and indicates an LBT parametercorresponding to transmission of the 8 UL subframes to the UE. In thiscase, if the UE fails to transmit the first 4 UL subframes and a lengthof the remaining UL TX burst corresponds to 4 UL subframes, in theaspect of the UE, it is preferable to apply an LBT parametercorresponding to the length of the 4 UL subframes.

In particular, if a UE fails to start transmission with an LBTparameter-based UL LBT operation indicated by a base station for aspecific UL TX burst, the present invention proposes a method for the UEto select an LBT parameter corresponding to a length of a (remaining) ULTX burst (or an MCOT value including the length of the UL TX burst) tobe transmitted and apply the selected LBT parameter to a UL LBToperation.

In particular, the present invention proposes various methods for a UEto transmit an uplink signal to a base station in a wirelesscommunication system supporting an unlicensed band.

According to an example of a method among the various methods, a UEreceives a signal for scheduling uplink transmission in an Nth subframe(N is a natural number) from a base station. If there is a currentlyperformed first LBT prior to the Nth subframe, the UE may continuouslyperform the first LBT (listen-before-talk) based on a specificcondition. Or, the UE performs a second LBT indicated to the Nthsubframe and performs uplink transmission based on a result of theperformed LBT.

In this case, the signal for scheduling the uplink transmission in theNth subframe can include information (e.g., LBT parameter information onthe second LBT) indicating the second LBT for the Nth subframe.

The specific condition indicates whether or not a first parameter forthe first LBT is different from a second LBT parameter for the secondLBT. If the first parameter for the first LBT is different from thesecond LBT parameter for the second LBT, the UE performs the second LBT.If the first parameter for the first LBT is identical to the second LBTparameter for the second LBT, the UE can continuously perform thecurrently performed first LBT. In particular, the UE can perform uplinktransmission based on a result of each of the LBTs performed by the UE.

Or, the specific condition may indicate whether or not the firstparameter for the first LBT has a contention window size greater than acontention window size of the second LBT parameter for the second LBT.In this case, if the first parameter for the first LBT does not have acontention window size greater than a contention window size of thesecond LBT parameter for the second LBT, the UE performs the second LBT.If the first parameter for the first LBT has a contention window sizegreater than a contention window size of the second LBT parameter forthe second LBT, the UE can continuously perform the currently performedfirst LBT. In particular, the UE can perform uplink transmission basedon a result of each of the LBTs performed by the UE.

Or, the specific condition may indicate whether or not a channel accesspriority class of the first parameter for the first LBT is equal to orgreater than a channel access priority class of the second LBT parameterfor the second LBT. In this case, if the channel access priority classof the first parameter for the first LBT is equal to or greater than thechannel access priority class of the second LBT parameter for the secondLBT, the UE can continuously perform the currently performed first LBT.If the channel access priority class of the first parameter for thefirst LBT is less than the channel access priority class of the secondLBT parameter for the second LBT, the UE terminates the first LBT andcan perform the second LBT. In particular, the UE can perform uplinktransmission based on a result of each of the LBTs performed by the UE.

In this case, if a first channel access priority class is greater than asecond channel access priority class, it may indicate that a priorityfor the first channel access priority class is lower than a priority forthe second channel access priority class.

Or, the specific condition may indicate whether or not a remainingbackoff counter value for the first LBT is equal to or less than abackoff counter value of the second LBT parameter for the second LBT. Inthis case, if the remaining backoff counter value for the first LBT isequal to or less than the backoff counter value of the second LBTparameter for the second LBT, the UE can continuously perform thecurrently performed first LBT. If the remaining backoff counter valuefor the first LBT is greater than the backoff counter value of thesecond LBT parameter for the second LBT, the UE can perform the secondLBT. In particular, the UE can perform uplink transmission based on aresult of each of the LBTs performed by the UE.

In this case, when the UE performs the second LBT, it may comprise thatthe UE initializes the first LBT operation and performs the second LBT.

In addition, if uplink transmission is performed in a subframe beforethe Nth subframe, the UE may perform uplink transmission in the Nthsubframe without an LBT operation.

Since it is able to include the examples for the proposed method as oneof implementation methods of the present invention, it is apparent thatthe examples are considered as a sort of proposed methods. Although theembodiments of the present invention can be independently implemented,the embodiments can also be implemented in a combined/aggregated form ofa part of embodiments. It may define a rule that an eNB informs a UE ofinformation on whether to apply the proposed methods (or, information onrules of the proposed methods) via a predefined signal (e.g., physicallayer signal or higher layer signal).

4. Device Configuration

FIG. 26 is a diagram illustrating configurations of a UE and a basestation capable of being implemented by the embodiments proposed in thepresent invention. The UE and the base station shown in FIG. 26 operateto implement the embodiments of a method of transmitting and receiving asignal between the UE and the base station.

A UE 1 may act as a transmission end on a UL and as a reception end on aDL. A base station (eNB) 100 may act as a reception end on a UL and as atransmission end on a DL.

That is, each of the UE and the base station may include a Transmitter(Tx) 10 or 110 and a Receiver (Rx) 20 or 120, for controllingtransmission and reception of information, data, and/or messages, and anantenna 30 or 130 for transmitting and receiving information, data,and/or messages.

Each of the UE and the base station may further include a processor 40or 140 for implementing the afore-described embodiments of the presentdisclosure and a memory 50 or 150 for temporarily or permanently storingoperations of the processor 40 or 140.

The UE 1 is configured to receive a signal for scheduling uplinktransmission in an Nth subframe (N is a natural number) via the receiver20 from the eNB 100. When there is a currently performed first LBT priorto the Nth subframe, if a channel access priority class of a first LBTparameter for the first LBT is equal to or greater than a channel accesspriority class of a second LBT parameter for a second LBT indicated forthe Nth subframe, the UE continuously perform the first LBT. When thereis a currently performed first LBT prior to the Nth subframe, if achannel access priority class of a first LBT parameter for the first LBTis less than a channel access priority class of a second LBT parameterfor a second LBT, the UE is configured to perform the second LBT. The UEcan be configured to perform uplink transmission via the transmitter 10based on an LBT result.

The Tx and Rx of the UE and the base station may perform a packetmodulation/demodulation function for data transmission, a high-speedpacket channel coding function, OFDM packet scheduling, TDD packetscheduling, and/or channelization. Each of the UE and the base stationof FIG. 26 may further include a low-power Radio Frequency(RF)/Intermediate Frequency (IF) module.

Meanwhile, the UE may be any of a Personal Digital Assistant (PDA), acellular phone, a Personal Communication Service (PCS) phone, a GlobalSystem for Mobile (GSM) phone, a Wideband Code Division Multiple Access(WCDMA) phone, a Mobile Broadband System (MBS) phone, a hand-held PC, alaptop PC, a smart phone, a Multi Mode-Multi Band (MM-MB) terminal, etc.

The smart phone is a terminal taking the advantages of both a mobilephone and a PDA. It incorporates the functions of a PDA, that is,scheduling and data communications such as fax transmission andreception and Internet connection into a mobile phone. The MB-MMterminal refers to a terminal which has a multi-modem chip built thereinand which can operate in any of a mobile Internet system and othermobile communication systems (e.g. CDMA 2000, WCDMA, etc.).

Embodiments of the present disclosure may be achieved by various means,for example, hardware, firmware, software, or a combination thereof.

In a hardware configuration, the methods according to exemplaryembodiments of the present disclosure may be achieved by one or moreApplication Specific Integrated Circuits (ASICs), Digital SignalProcessors (DSPs), Digital Signal Processing Devices (DSPDs),Programmable Logic Devices (PLDs), Field Programmable Gate Arrays(FPGAs), processors, controllers, microcontrollers, microprocessors,etc.

In a firmware or software configuration, the methods according to theembodiments of the present disclosure may be implemented in the form ofa module, a procedure, a function, etc. performing the above-describedfunctions or operations. A software code may be stored in the memory 180or 190 and executed by the processor 120 or 130. The memory is locatedat the interior or exterior of the processor and may transmit andreceive data to and from the processor via various known means.

Those skilled in the art will appreciate that the present disclosure maybe carried out in other specific ways than those set forth hereinwithout departing from the spirit and essential characteristics of thepresent disclosure. The above embodiments are therefore to be construedin all aspects as illustrative and not restrictive. The scope of thedisclosure should be determined by the appended claims and their legalequivalents, not by the above description, and all changes coming withinthe meaning and equivalency range of the appended claims are intended tobe embraced therein. It is obvious to those skilled in the art thatclaims that are not explicitly cited in each other in the appendedclaims may be presented in combination as an embodiment of the presentdisclosure or included as a new claim by a subsequent amendment afterthe application is filed.

The embodiments of the present invention can be applied to variouswireless access systems including 3GPP (3rd Generation PartnershipProject) and 3GPP2 system. The embodiments of the present invention canbe applied not only to various wireless access systems but also to alltechnical fields to which the various wireless access systems areapplied. Further, the proposed method can also be applied to an mmWavecommunication system using ultrahigh frequency band.

What is claimed is:
 1. A method of a user equipment (UE) in a wirelesscommunication system supporting an unlicensed band, the methodcomprising: performing a channel access procedure (CAP) based on a firstchannel access priority class parameter; receiving, from a base station(BS) a signal including a second channel access priority class parameterand scheduling information for uplink transmission in a specific timeresource; performing the CAP based on the first channel access priorityclass parameter continuously based on that the first channel accesspriority class parameter is equal to or greater than the second channelaccess priority class parameter indicated in the signal; performing theCAP based on the second channel access priority class parameterindicated in the signal based on that the first channel access priorityclass parameter is less than the second channel access priority classparameter; and performing uplink transmission based on a result of theperformed CAP, wherein the CAP based on the first channel accesspriority class parameter is being performed before the specific timeresource.
 2. The method of claim 1, wherein performing the CAP based onthe second channel access priority class parameter indicated in thesignal comprises terminating the CAP based on the first channel accesspriority class parameter.
 3. The method of claim 1, wherein based onthat the uplink transmission is performed prior to the specific timeresource, performing uplink transmission in the specific time resourcewithout the CAP.
 4. The method of claim 1, wherein the first channelaccess priority class parameter comprises at least one of a firstcontention window size, a first maximum channel occupancy time, a firstback-off counter or a first channel access priority class value, andwherein the second channel access priority class parameter comprises atleast one of a second contention window size, a second maximum channeloccupancy time, a second back-off counter or a second channel accesspriority class value.
 5. A user equipment (UE) in a wirelesscommunication system supporting an unlicensed band, the UE comprising: areceiver; a transmitter; and a processor configured to operate in amanner of being connected with the receiver and the transmitter, whereinthe processor configured to: perform a channel access procedure (CAP)based on a first channel access priority class parameter; receive, froma base station (BS) a signal including a second channel access priorityclass parameter and scheduling information for uplink transmission in aspecific time resource; perform the CAP based on the first channelaccess priority class parameter continuously based on that the firstchannel access priority class parameter is equal to or greater than thesecond channel access priority class parameter indicated in the signal;perform the CAP based on the second channel access priority classparameter indicated in the signal based on that the first channel accesspriority class parameter is less than the second channel access priorityclass parameter; and perform uplink transmission based on a result ofthe performed CAP, wherein the CAP based on the first channel accesspriority class parameter is being performed before the specific timeresource.
 6. The UE of claim 5, wherein the processor terminates the CAPbased on the first channel access priority class parameter whenperforming the CAP based on the second channel access priority classparameter indicated in the signal.
 7. The UE claim 5, wherein based onthat the uplink transmission is performed prior to the specific timeresource, the processor performs uplink transmission in the specifictime resource without the CAP.
 8. The UE of claim 5, wherein the firstchannel access priority class parameter comprises at least one of afirst contention window size, a first maximum channel occupancy time, afirst back-off counter or a first channel access priority class value,and wherein the second channel access priority class parameter comprisesat least one of a second contention window size, a second maximumchannel occupancy time, a second back-off counter or a second channelaccess priority class value.